1. Field of the Invention
The present invention relates to an information recording and reproducing apparatus with high recording density.
2. Description of the Related Art
In recent years, small-sized portable equipment has been diffused in the world. At the same time, following the great development of high-speed information transport network, demands of small-sized large-capacity nonvolatile memories have rapidly expanded. Above all, in NAND type flash memories and small-sized HDDs (hard disk drives), the recording density has rapidly developed, leading to the formation of a large market.
Under these backgrounds, some ideas of novel memories aiming to greatly exceed the limits of recording density are proposed.
For example, transition metal element-containing ternary oxides such as perovskite and spinel (see, for example, JP-A-2005-317787 and JP-A-2006-80259); binary oxides of a transition metal (see, for example, JP-A-2006-140464); and the like are studied. In case of using such a material, a principle in which a low-resistance state (ON) and a high-resistance state (OFF) can be repeatedly changed by application of a voltage pulse, and these two states are made corresponding to binary data of “0” and “1” to record the data is employed.
With respect to writing/erasing, for example, a method in which a pulse is applied in a reverse direction to each other with respect to the time of changing from the low-resistance state to the high-resistance state and the time of changing from the high-resistance state to the low-resistance state is employed in ternary oxides. On the other hand, in binary oxides, there may be the case where the writing/erasing is performed by applying a pulse having a different pulse amplitude or pulse width.
With respect to readout, it is performed by making a readout current flow to an extent that the writing/erasing does not occur in a recording material and measuring an electrical resistance of the recording material. In general, a ratio of the resistance in the high-resistance state and the resistance in the low-resistance state is about 103.
The greatest merit of such materials resides in the matter that even when a device size is reduced to about 10 nm, the recording material is theoretically operable. In that case, since a recording density, of about 10 Tbpsi (terabits per square inch) can be realized, such is considered to be one of candidacies for high recording density.
As to an operation mechanism of such novel memories, the following are proposed. As to perovskite materials, diffusion of oxygen deficiency, charge accumulation in an interface level and the like are proposed. On the other hand, as binary oxides, diffusion of an oxygen ion, Mott transition and the like are proposed. Though it is hard to say that the details of the mechanism have been elucidated, since the same change in the resistance is observed in various material systems, such is noticeable as one of candidacies for high recording density.
Besides, MEMS (micro electro mechanical systems) memories using an MEMS technology are proposed. The greatest merit of such MEMS memories resides in the matter that the recording density can be tremendously enhanced because it is not necessary to provide a wiring in each recording part for recording a bit data. As to a recording medium and a recording principle, various proposals are made. By combining the MEMS technology with a new recording principle, attempts to achieve large improvements regarding consumption electric power, recording density, operation speed, etc. are made.
However, a novel information recording medium using such a new recording material has not been realized yet. As one of reasons for this, it is pointed out that the consumption electric power is large and that the heat stability in each resistance state is low (see, for example, S. Seo, et al., Applied Physics Letters, Vol. 85, pp. 5655-5657 (2004)).